but a question like the OP's was brought up not to long ago on CF boards and that person was redirected to some things that Rob wrote when he answered a question on a person trying to do too much and not losing body fat around the abdominal area due to cortisol and some other things

High stress (mental, physical, lack of sleep, lack of food) will never be good. If you are losing weight in a high stress environment of low calories and high activity level (like boot camp) you will get lean....and then once refeeding happens down the road the bodyweight will self-regulate itself back up storing more fat (stubborn). Hence all the yo-yo crash dieters.

If you already have stubborn fat, increasing stress more is not going to help and only create more and more of it. Hence why IF can work, but not with someone that has fitness ADD working out 7x/wk at high intensity while eating 800cal/day and sleeping 4 hours/night.